The invention relates to the recycle of basic hydrogen peroxide for use in a chemical oxygen iodine laser (COIL) system. More particularly, the invention relates to the purification of a potassium chloride stream recycled from spent COIL fuel.
Basic hydrogen peroxide (BHP) is a principle fuel used in the operation of chemical oxygen-iodine lasers (COIL). COIL lasers are short wavelength high-power chemical lasers with wide ranging industrial, technological, and military applications. COIL lasers, which are electronic transitional lasers, are favored over vibrational or rotational transition lasers because they have one of the best beam qualities of any available laser, which allows for clean cuts and welds, as well as simple splitting and direction. In addition, the COIL laser has greater scalability than photolytic and solid state devices.
BHP is generated by the combination of alkali hydroxide, typically potassium hydroxide, with hydrogen peroxide according to the formula:
OHxe2x88x92+H2O2+M+xe2x86x92O2Hxe2x88x92+H2O+M+xe2x80x83xe2x80x83(I) 
where M represents an alkali metal such as lithium, sodium or potassium or combination thereof. BHP is the dissociated solution of H2O2 and MOH. In practice, the term BHP typically refers to a solution having 4 molar to 8 molar concentration of perhydroxyl ion (O2Hxe2x88x92).
To power the laser, the perhydroxyl ions and alkali ions of the BBP solution are reacted with chlorine gas according to the formula:
Cl2+2O2Hxe2x88x92+2M+xe2x86x92H2O2+2MCl+O2(1xcex94)xe2x80x83xe2x80x83(II) 
The gaseous product stream of reaction II is used as a fuel feed to a COIL laser. The singlet delta oxygen (O2(1xcex94)) of the fuel feed is combined with a source of iodine, where the excited state oxygen causes rapid dissociation of the iodine. The iodine atoms, excited by reaction with the singlet delta oxygen, release energy in the form of light. Thus, the excited state iodine is the gain medium for the chemical laser.
A feed containing singlet delta oxygen is utilized as fuel for the laser until the readily usable quantities of O2(1xcex94) have been depleted. After being used in the lasing process, the remaining by-products of H2O2, KCl, KOH, and water are recycled to form fresh BHP. Typically, the spent fuel stream will be at a temperature below the freezing point of water. The KCl in the spent fuel, which is only sparingly dissolved below xe2x88x9220xc2x0 C., is separated from the H2O2 and KOH components of the stream. Water may also be removed from the spent BHP. The liquid stream of H2O2 and KOH is recycled as a fresh BHP stream and combined with chlorine to produce additional singlet delta oxygen. The water and KCl from the spent fuel are heated such that the water melts and dissolves the KCl to form a brine solution. The brine solution may be fed to a chloralkali cell which uses electrolysis to produce KOH, H2, and Cl2.
In practice, the use of recycled KCl solution with a chloralkali cell for use in a COIL system is often less efficient than would be expected. In theory, the operation of the cell should be similar to the sodium based NaCl to NaOH chloroalkali cell which is common in the art of caustic soda production. However, the chloralkali cells which use recycled KCl feeds have been plagued with low levels of conversion, performance degradation, and production rate deterioration. Until now, the problems unique to chloralkali cells used in COIL recycle systems have not been explored. What is needed is a method for improving the performance of chloralkali cells used in COIL systems.
It has been found that when solid alkali chloride, typically KCl, and solid H2O (ice) are recovered from the spent BHP stream of a COIL device, the stream of recovered alkali chloride and water contains remnants of BHP, i.e. an alkali base, H2O2, and dissociation products thereof, within or on their solid forms. Therefore, if a stream of recovered alkali chloride solution is recycled to a chloralkali reactor, the reactor also receives small amounts of BHP components. It has been experimentally determined that the BHP components within the recycled KCl stream form unwanted products within the chloralkali cell, such as O2, HCl, and ClO3xe2x88x92.
For instance, unwanted KOH within the recycled KCl stream reacts with Cl2 at the anode of the chloralkali cell to form OClxe2x88x92, which is further oxidized at the anode to form ClO3xe2x88x92. Each such undesired oxidation which occurs at the anode of the cell decreases the efficiency of the cell. Formation of such unwanted products reduces the efficiency and yield of the chloralkali cell, thereby adversely impacting the overall efficiency of the COIL process.
The current invention is a method and apparatus for removing BHP contaminants from a recycled alkali chloride solution stream before the stream is fed to a chloralkali cell so that the contaminants do not enter the chloralkali cell and do not cause the wasteful production of unwanted byproducts. Via a number of reaction steps, unwanted KOH within the recycled brine solution is reacted with chlorine gas and converted into KCl, which is useful in the operation of the chloralkali cell, and oxygen gas, which is outgassed from the system. When sufficient quantities of both KOH and H2O2 are present within the recycled brine stream, the main reaction of the invention proceeds according to Equation (1):
2KOH(aq)+H2O2(aq)+Cl2(g)xe2x86x92O2(g)+2KCl(aq)+2H2O(l)xe2x80x83xe2x80x83(1) 
Because twice the amount of KOH reactant is consumed than H2O2 according to Equation (1), the brine solution will contain residual H2O2 after elimination of the KOH components. Any H2O2 remaining in the recycled KCl stream after elimination of the KOH is reacted with chlorine to form HCl and oxygen gas according to Equation (2).
H2O2(aq)+Cl2(g)xe2x86x92O2(g)+2HCl(aq)xe2x80x83xe2x80x83(2) 
The HCl lowers the pH of the brine solution, after which the pH may be adjusted by the addition of supplemental KOH according to the acid base Equation (3).
HCl(aq)+KOH(aq)xe2x86x92KCl(aq)+H2O(l)xe2x80x83xe2x80x83(3) 
The result of the invented method is a recycled brine solution stream wherein substantially all KOH and H2O2 contaminants are removed prior to the stream being fed to the chloralkali cell of a BHP production system.
The invented apparatus is a reactor which uses components of the COIL process, namely KOH and Cl2, to pretreat a recycled brine anolyte stream before the recharged brine anolyte is supplied to the chloralkali cell, according to the above described process.